devctl (alike?) for devfs

[Andriy Gapon]

Maybe this is a crazy idea or maybe we already have something like this.
Is it possible to get notifications about changes in devfs - appearance
and disappearance of devices (in devfs sense of the word)?
devctl currently notifies about real (hardware) devices handled by
device drivers and some notifications about hardware/driver events.
But what if I want to automatically run some action if
/dev/ufs/magic-label appears?
Or if I want to monitor appearance and disappearance of ad* and da*
devices (without having to monitor low level drivers like umass)?

-- 
Andriy Gapon